Aircrafts require a landing gear for landing and taking-off. Term aircraft relates to all kinds of fixed-wing and rotary-wing aircraft. Airplanes are fixed-wing aircrafts that conventionally land on and take-off on runways. Land airplanes (operate on land or solid ground) comprise fixed or retractable landing gear. The retractable landing gear is retracted inside the fuselage to reduce an aerodynamic drag after the take-off or during the flight. (However fixed landing gear is not retractable.) The retractable landing gear must be deployed or in landing position when landing on the runway.
A seaplane is a powered fixed-wing aircraft capable of taking off and landing (alighting) on water. Seaplanes are either flying boats or floatplanes. In a flying boat, the main source of buoyancy is the fuselage, which acts like a ship's hull in the water because the fuselage's underside has been hydrodynamically shaped to allow water to flow around it. A floatplane has slender pontoons, or floats, mounted under the fuselage. Two floats are common, but other configurations are possible. Only the floats of a floatplane normally come into contact with water. The fuselage remains above water.
However, there are also amphibious airplanes and they can operate on ground (runways) or water. Amphibious airplanes comprise a conventional wheeled type landing gear for landing on ground and pontoon structures or “floats” for water landing. For landing on runways or ground, the conventional landing gear must be in landing position or landing configuration so that it is extended below the airplanes pontoon structures. And for landing on water, this landing gear must be retracted, so that landing on water happens with pontoons/floats. In such case landing gear is typically retracted inside the fuselage, wings or pontoons. Thereby amphibious airplanes have two configurations for landing gear depending on the landing surface type.
When amphibian (amphibious aircraft) lands on ground with landing wheels retracted, the plane will make contact with the runway with pontoons. This causes some damage to the parts of the plane and to the pilot's self-esteem. Usually the damages are minor in such case.
On the other hand, when the amphibian is landing on water and the landing gear is extended, the aircraft will typically flip forward into the water upon the landing gear's contact with the water. This causes damage to the aircraft and injury to the crew and passengers. The damages to the amphibian in such event are usually severe: The plane will decelerate and stop within very short distance, flip over on its back into the water. Damages are caused by the rapid deceleration, water entering electronic equipment and engine while it is running. Such damages can result in scrapping the plane completely.
One of the biggest causes for accidents and the largest source of insurance claims for amphibious aircraft are related to the improper landing gear configuration when landing on a certain type landing surface. Amphibian pilots are particularly susceptible to committing gear status errors due to the difference in the proper gear status for any landing surface; any pilot can make such a mistake.
Therefore, amphibians nowadays comprise different type warning systems to help the pilot to take care of proper landing gear configuration when landing an amphibious aircraft.
From the prior art is known U.S. Pat. No. 4,516,124, which discloses an advisory system for the pilot of an amphibious aircraft with retractable landing gear for checking the status of the landing gear. The apparatus senses changes in aircraft speed indicative of an imminent landing and prompts the pilot to verify that the landing gear is in a position compatible with the type of surface, land or water, chosen for landing.
From the prior art is also known US2006226286, which discloses system for controlling landing gear of an aircraft. The system comprises a sensor for sensing water, and the sensor is coupled to the landing gear to retract so as to retract the landing gear when the sensor senses a body of water. The system operates during the contact of landing and operates as kind of anti-flip system.
From the prior art is also known US2003011493, which discloses an aircraft landing gear warning apparatus. The apparatus comprises a computer operatively connected to a surface monitor and a gear-status warning indicator. Preferably the surface monitor is a laser distance measuring system. However any sensing subsystem which is capable of determining the altitude of the aircraft is suitable, although preferably the sensing subsystem also indicates the landing surface (e.g., ground or water). The computer also accepts an input from the gear status sensors to determine if the landing gear is extended or retracted. If the system senses a water surface and the landing gear is down, a warning alerts the pilot that the landing gear is in the incorrect configuration.
In an embodiment of US2003011493, the surface monitor is comprised of two laser distance-measuring systems. A first laser distance measuring system is used to emit a narrow laser beam, which provides a good return when reflected off of land. A second laser distance measuring system is used to emit a spread laser beam, which provides a good return when reflected off of water. In operation both the first and second laser distance measuring systems would emit laser beams continuously.
There are however some disadvantages relating to the known prior art, such as still occurring accidents caused by improper landing gear configuration when landing, despite of the presence of warning or advisory systems. A major portion of amphibious aircraft landing accidents is caused by improper landing gear configuration/position during landing.
The drawback of advisory systems, like U.S. Pat. No. 4,516,124, is that they operate every time plane is landing or about to land and require pilot input for selecting the landing surface type. This causes that the pilot has to manually operate the system every time, which creates an autonomic reactions to silence the system without consciously making the selections for the respective landing surface type.
Another drawback for anti-flip systems for preventing the flipping the amphibian, is that these systems operate at the moment of the contact with landing surface. This means that pilot error has already occurred. In such case the outcome depends on the operation and reliability of the anti-flip system.
Yet another drawback relates to warning systems that are comprised of two laser-distance measuring systems, of which first one emits narrow laser beam and second one emits spread laser beam. These systems may give erroneous warnings when there is water on runway or when landing on shallow water and bottom reflects a confusing signal. Furthermore, these systems are susceptible for dirt that causes weakening of the signal or the measurement.